1. Field of the Invention
The present invention concerns a contact exposure device used in contact exposure processes, especially a contact exposure device for exposing a mask pattern on a workpiece like a flexible printed circuit (FPC) having polyimide properties that is thin and prone to cracking. More specifically, the invention relates to a contact exposure device provided with an interval setting means that separates and mutually faces a mask and workpiece so as to have a preset contact-free interval when pressure between a mask and workpiece is reduced.
2. Description of Related Art
Exposure processes in which light passing through a mask is irradiated on a workpiece to expose a mask pattern on a workpiece are carried out to form various types of electronic devices on a workpiece in the production of various electrical components that require microsize processing, such as semiconductor devices, liquid crystal substrates, micro-machines, etc. Among aforementioned exposure methods, the contact exposure method is one that adheres a mask and workpiece and then copies a mask pattern onto the workpiece.
FIGS. 7(a) and 7(b) are diagrams showing the structure of a contact exposure device. The diagram shows the structure of a contact exposure device that adheres a mask and workpiece by applying force through decompression that pushes a photomask (hereinafter abbreviated mask M) and a workpiece W together, followed by exposure. FIG. 7(a) is a top view while FIG. 7(b) is a sectional view along line Axe2x80x94A of FIG. 7(a).
In the diagram, positioning member 1 of mask M is mounted on a mask stage MS and an aperture 2 is formed in mask stage MS so that exposure light from a photo-irradiation unit (not shown) will be irradiated on workpiece W through mask M.
Mask M on which a mask pattern is formed is brought into contact with the positioning member 1 and is laid on aperture 2 of mask stage MS. A vacuum groove 3 extends about the periphery of aperture 2 of mask stage MS, and mask M is attached/held by vacuum that is provided to vacuum groove 3 from a vacuum source (not shown). In addition, a conduit 4 for depressurization of the space that is formed by photomask M, mask stage MS, workpiece W, workpiece stage WS and vacuum seal unit 6 is provided in the mask stage MS.
A groove 5 for drawing a vacuum to attach workpiece W is formed in workpiece stage WS and the workpiece W that is placed on the workpiece stage WS is attached/held on the workpiece stage WS by vacuum that is supplied to vacuum groove 5 from a vacuum source (not shown). Vacuum seal unit 6 comprises a sealing member formed, for example, from rubber, that is mounted about the periphery of workpiece stage WS and is useful for creating a vacuum state to adhere mask M to workpiece W.
In addition, the workpiece stage WS is attached to workpiece stage drive mechanism 8 via interval setting groove 7. Workpiece stage drive mechanism 8 moves workpiece stage WS in the X direction (for example, left-right direction of FIG. 7(b)), Y direction (for example, perpendicularly to the plane of paper in FIG. 7(b)) and Z direction (up-down in FIG. 7(b)), and rotates workpiece stage WS about an axis perpendicular to the plane of workpiece W. The shape of workpiece stage W is usually created to match the shape of workpiece W. It is round if the workpiece is round and aperture 2 also is polygonal if the workpiece is polygonal.
Exposure of workpiece W by the contact exposure device shown in of FIGS. 7(a) and 7(b) is explained below.
(1) Mask M is brought into contact with positioning member 1 and is placed on the mask stage MS. Next, a vacuum is supplied to vacuum groove 3 and the mask M is attached/held to the mask stage MS.
(2) Workpiece W is placed on the workpiece stage WS, a vacuum is supplied to the groove 5 from a vacuum source and workpiece W is attached/held on workpiece stage WS.
(3) Workpiece stage WS is raised by workpiece stage drive mechanism 8 and the workpiece W is brought into contact with mask M. Mask M and workpiece W are then positioned in parallel by interval setting groove 7 (consult the gazette of Japanese Kokai Publication Hei-7-74096 and corresponding U.S. Pat. No. 5,543,890 for parallel positioning of mask M and workpiece W).
(4) Following parallel positioning of mask M and workpiece W, the workpiece stage WS is lowered slightly and the gap between mask M and workpiece S is set to an alignment gap. An alignment mark inscribed on mask M and workpiece S is detected by an alignment microscope (not shown), and workpiece stage WS is moved in XYxcex8 directions the by workpiece stage drive mechanism 8 so that both alignment marks coincide, thereby completing alignment of mask M and workpiece W.
(5) Following completion of alignment, workpiece stage WS is elevated to bring mask M into contact with the workpiece W.
Here, mask M and workpiece W are merely brought into mutual contact. Mask M and workpiece W cannot be adhered along the entire surface if slight unevenness or warping are present on the mask M and workpiece W. Accordingly, unevenness may develop in the gap between mask M and workpiece W in some cases, as shown in an exaggerated manner in FIG. 8.
When exposure is carried out in the aforementioned state, the exposure accuracy following exposure processing (pattern shape following developing) varies with the site of the exposure region. Thus, force is applied between mask M and workpiece W so as to push them together, as explained below, since mask M and workpiece W are adhered over the entire surface.
(6) Vacuum seal unit 6 mounted about the periphery of workpiece stage WS contacts the lower surface of mask stage MS when workpiece stage WS is raised and mask M is brought into contact workpiece W. A sealing space is created by mask M, mask stage MS, workpiece W, workpiece stage WS and vacuum seal unit 6. A vacuum is supplied to conduit 4 mounted in mask stage MS in this state and the aforementioned sealing space is depressurized.
(7) Upon depressurization of the sealing space, mask M is pushed against workpiece W and mask M is adhered to workpiece W over the entire surface, as shown in FIG. 9.
(8) Workpiece W is irradiated through mask M by a photo-irradiation unit with light containing exposure light while mask M is adhered to workpiece W as mentioned above to complete exposure.
In conventional contact exposure, as mentioned above, the space between mask M and workpiece W is depressurized, force is applied to mask M and the shape of mask M is altered so as to match the shape of the workpiece W. Workpiece W is then held between mask M and workpiece stage WS and adhered. However, if even a slight amount of dirt is present on workpiece stage WS in the aforementioned conventional example, the workpiece W would be deformed as shown in FIG. 10. Accordingly, force would be concentrated at the section of contact between mask M and the deformed section of workpiece W when mask M is adhered to workpiece W, and the expensive mask M would be damaged. Exposure using a damaged mask would result in the copying of that damage directly to workpiece W, resulting in a defective product.
Furthermore, there is a danger of the workpiece W breaking since a concentrated force is applied even to deformed sections of workpiece W. In particular, thin workpieces W having thickness on the order of 100 to 50 xcexcm, like flexible printed circuits (FPC) having polyimide properties, have come into use in recent years while a tendency to increased contact force between mask M and workpiece W has developed accompanying the demand for high resolution. This has increased the danger of breakage of the workpiece W.
Thus, the inventors have proposed a method of contact exposure which separates and mutually faces a mask and workpiece so that the two maintain a gap without contact upon depressurization of the space between mask and workpiece to a level of force that permits the desired contact force to be reached. The space between a mask and workpiece is depressurized, the two are brought together, and the workpiece is then floated up by air from the workpiece stage to adhere the mask to the workpiece. That is followed by exposure. (See the gazette of Japanese Kokai Publication Hei-10-1 19032, U.S. patent application Ser. No. 09/299,748 and published European Patent Application EP 0953878A.
FIG. 11 is a diagram showing the structure of a contact exposure device that completes the aforementioned contact exposure. The sections that are identical with those in FIG. 7 have the same notation.
Vacuum groove 3 is mounted about the periphery of the aperture in the mask stage MS in FIG. 11. Mask M is attached/held on mask stage MS by vacuum that is supplied to vacuum adsorption groove 3 that is mounted on the surface of mask stage MS. Furthermore, conduit 4 is provided in mask stage MS so as to depressurize the space A that is formed by mask M, mask stage MS, workpiece W, workpiece stage WS and vacuum seal unit 6. Groove 5 is provided in the workpiece stage WS to attach workpiece W to workpiece stage WS and to float the workpiece W by blowing a gas, such as air, against the workpiece W.
The groove 5 is connected to vacuum pump 11, compressor 12 via valves V1, V2. Workpiece W is attached/held on workpiece stage WS by closing valve V2 and opening the valve V1 and then drawing a vacuum in the groove 5. In addition, the workpiece W is floated by providing air from compressor 12 to the groove 5 by closing valve V1 and opening valve V2, so that the workpiece W is pushed against the side of mask M (the provision of air to the workpiece stage W and the floating of the workpiece W from workpiece stage WS is termed back-blow of the workpiece W).
The vacuum seal unit 6 comprises a sealing member formed, for example, of rubber, that is mounted about the periphery of workpiece stage WS and is useful for creating a vacuum state to adhere the mask M to the workpiece W.
In addition, just as in FIG. 6, the workpiece stage WS is attached to a workpiece stage drive mechanism (not shown) via an interval setting groove (not shown). The workpiece stage drive mechanism moves workpiece stage WS in the X direction (for example, left-right direction of the diagram), Y direction (for example, perpendicularly to the plane of paper in the diagram), and Z direction (up-down in the diagram), and rotates workpiece stage WS about the axis perpendicular to the plane of workpiece W. Furthermore, the interval setting means 10 that sets a gap between the mask M and the workpiece W (hereinafter abbreviated backup ring 10) is mounted about the periphery of workpiece stage WS. The upper surface of backup ring 10 is finely machined. When workpiece stage WS floats, the upper surface of backup ring 10 makes contact with the lower surface of mask stage MS.
The backup ring 10 functions as follows.
[1] The lower surface of mask M and the upper surface of workpiece W are separated and mutually faced at a prescribed gap by bringing backup ring 10 into contact with the lower surface of the mask stage.
[2] The movement of workpiece stage WS in the direction of mask stage MS during depressurization of sealing space A is prevented by pushing at atmospheric pressure. As a result, gap D between workpiece W and mask M can be shortened during depressurization of sealing space A as compared to the distance during aforementioned separation and mutual facing, and the mask and workpiece can be held at a distance such that contact is not made.
[3] Workpiece stage WS and mask stage MS are held in parallel. Contact exposure in FIG. 11 is carried out as follows.
The alignment gap between mask M and workpiece W is set following parallel positioning of mask M and workpiece W by bringing the lower surface of mask stage MS into contact with the upper surface of backup ring 10 to complete alignment between a mask and workpiece.
Next, workpiece stage WS is elevated and backup ring 10 is brought into contact with the lower surface of mask stage MS. In this state, the space between mask M and workpiece W is depressurized to the force capable of attaining the desired contact force. Mask M flexes in the direction of workpiece W upon depressurization of the space between mask M and workpiece W, but mask M and workpiece W do not make contact since backup ring 10 lies between mask stage MS and workpiece stage WS and the desired gap can be maintained. Subsequently, workpiece W is floated by air from workpiece stage WS (back-blow of workpiece W), mask M and workpiece W are adhered and then exposed.
By adopting the aforementioned technique, a mask and workpiece can be adhered and exposed without fear of damaging the mask and without breaking the workpiece.
Incidentally, backup ring 10 must be selected such that the height of gap D reaches a prescribed value as a function of the thickness of workpiece W when processing workpiece W having different thicknesses, as shown in FIG. 11. However, backup ring 10 is usually attached to workpiece stage WS by a screw. Replacement of backup ring 10 requires releasing the screw and detaching backup ring 10, followed by setting a new backup ring in place and screwing it in. The problem is that this replacement operation takes time. Furthermore, the need to prepare a plurality of backup rings imposes an added expense, and an additional problem is the need to secure a storage site for them.
The present invention was devised in light of aforementioned circumstances. It provides a contact exposure device which does not require replacement of a backup ring even when processing workpieces of different thicknesses.
To solve aforementioned problem, the present invention comprises a first member in which an interval setting means commensurate with aforementioned backup ring is attached to a workpiece stage or a mask stage, and a second member that can move vertically relative to the first member. As a result, the interval between the mask and workpiece can be adjusted to the prescribed value without replacing the interval setting means when treating workpieces of varying thicknesses.
Accordingly, the backup ring need not be replaced when processing workpieces of different thickness as in a conventional example, and that permits the operational efficiency to be improved. Furthermore, replacement backup rings need not be prepared and that permits the cost to be reduced.